Ticks

Published: 07/01/2010

Tick is the common name for the small arachnids that, along with mites, constitute the order Acarina. Ticks are external parasites which live off the blood of mammals, birds, and occasionally reptiles and amphibians. Ticks are important carriers of a number of diseases, and second only to mosquitoes as carriers of human disease.
Human disease: Hard ticks can transmit human diseases such as relapsing fever, Lyme disease, Rocky Mountain spotted fever, tularemia, equine encephalitis and several forms of ehrlichiosis. Additionally, they are responsible for transmitting livestock diseases, including babesiosis and anaplasmosis.
Habitat: Ticks are often found in tall grass, where they will rest themselves at the tip of a blade so as to attach themselves to a passing animal or human. It is a common misconception that the tick can jump from the plant onto the host. Physical contact is the only method of transportation for ticks. They will generally drop off of the animal when full, but this may take several days. Ticks contain a structure in their mouth area that allows them to anchor themselves firmly in place while sucking blood. Pulling a tick out forcefully may squeeze contents of the tick back into the bite and often leaves the mouthpiece behind, which may result in infection.
Eggs: Eggs laid by an adult female deer tick in the spring hatch into larvae later in the summer. These larvae reach their peak activity in August. No bigger than a newsprinted period, a larva will wait on the ground until a small mammal or bird brushes up against it. The larva then attaches itself to its host, begins feeding, and engorges with blood over several days.
Lyme disease: If the host is already infected with the Lyme disease spirochete from previous tick bites, the larva will likely become infected as well. In this way, infected hosts in the wild serve as spirochete reservoirs, infecting ticks that feed upon them. Other mammals and ground-feeding birds may also serve as reservoirs.
Most larvae, after feeding, drop off their hosts and molt, or transform, into nymphs in the fall. The nymphs can remain active throughout the winter and early spring.
Nymphs: In May, host-seeking nymphs wait on vegetation near the ground for a small mammal or bird to approach. The nymph will then latch on to its host and feed for 4 or 5 days, engorging with blood and swelling to many times its original size. If previously infected during its larval stage, the nymph may transmit the Lyme disease spirochete to its host. If not previously infected, the nymph may become infected if its host carries the Lyme disease spirochete from previous infectious tick bites.
Human hosts: Too often, humans are the hosts that come into contact with infected nymphs during their peak spring and summer activity. Although the nymphs' preferred hosts are small mammals and birds, humans and their pets are suitable substitutes. Because nymphs are about the size of a poppy seed, they often go unnoticed until fully engorged, and are therefore responsible for the majority of human Lyme disease cases.
Engorged nymph: Once engorged, the nymph drops off its host into the leaf litter and molts into an adult. These adults actively seek new hosts throughout the fall, waiting up to 3 feet above the ground on stalks of grass or leaf tips to latch onto deer (its preferred host) or other larger mammals (including humans, dogs, cats, horses, and other domestic animals). Peak activity for adult deer ticks occurs in late October and early November.
Winter: As winter closes in, adult ticks unsuccessful in finding hosts take cover under leaf litter or other surface vegetation, becoming inactive when covered by ice and snow. Generally, winters in the northeast and upper mid-west are cold enough to keep adult ticks at bay until late February or early March but not when temperatures begin to rise. At this time, they resume the quest for hosts in a last-ditch effort to obtain a blood meal allowing them to mate and reproduce.
Adult female ticks that attach to deer, whether in the fall or spring, feed for approximately one week. Males feed only intermittently. Mating may take place on or off the host, and is required for the female's successful completion of the blood meal. The females then drop off the host, become gravid, lay their eggs underneath leaf litter in early spring, and die. Each female lays approximately 3,000 eggs. The eggs hatch later in the summer, beginning the two-year cycle anew.